Summary of Work: Patients with failed parathyroid surgery require localization prior to subsequent operation. When the noninvasive studies (computer tomography, US, magnetic resonance imaging, sestamibi) are negative, arteriography and venous sampling are performed. Venous sampling is the most accurate of the localizing studies, but it is quite tedious and involves 25 to 30 blood samples. In an attempt to simplify the procedure, we have begun to measure elevated levels of parathyroid hormone (PTH) following selective arteriogram as a means of localizing parathyroid pathology without the need for parathyroid venous sampling. Preliminary laboratory evidence demonstrated that nonionic contrast material perfusing a parathyroid vascular bed results in a similar release of PTH hyperplastic and adenomatous parathyroid tissue response. A catheter placed in the SVC obtains samples before and at 20, 40, and 60 seconds after selective arteriography of the internal mammary artery, inferior thyroid artery and superior thyroid artery. A 1.4 x elevation of PTH on the 20-to 40-second samples localizes parathyroid pathology to the distribution of the injected vessel. We have just reported results for our first 20 patients. The test was positive in IS (75%), which could have obviated the need for parathyroid venous sampling. However, all patients will undergo routine venous sampling until the specificity of the arterial stimulation is determined. There have been no complications associated with this protocol and continued accrual of all patients needing invasive parathyroid localization is planned.